Not Applicable
Not Applicable
1. Field of the Invention
This invention relates to video surveillance systems and more particularly to video surveillance systems using motion video camera arrays.
2. Description of the Related Art
There are several shortcomings in the current video surveillance systems that need to be overcome before complete video coverage becomes commonplace. Generally, installation and materials cost of individual video cameras is prohibitively high to permit complete video coverage of an installation or facility to be placed under surveillance. Motion video cameras used for video surveillance generally use CCD based technology, expensive lenses and enclosures. Therefore, in one solution, cameras are strategically mounted to cover thoroughfares and sensitive areas. In a retail store, for example, a fixed mount motion video camera may be placed over the main entrance, another strategically placed to cover the cash register and countertop, and another to cover expensive or easily concealed merchandise. These placements may be foiled because line-of-sight is not ideal for a particular event, or an irregular activity occurs elsewhere in the store where coverage does not exist.
In another solution, servo-controlled movable cameras are used in which line-of-sight may be remotely altered by a human operator or tracking algorithm. Movable cameras have the ability to be steered and even zoomed into an area of interest. However, each movable camera is significantly more expensive than a number of fixed mount cameras, and generally requires a human operator.
In all of the present solutions, cabling costs for each camera typically requires a power cable as well as coaxial cable for the video signals. Servo-controlled movable cameras also require cabling to support the remote camera control interface. The cabling and mounting costs may often exceed the unit cost of individual cameras.
In addition, when a number of cameras are placed, a device called a video multiplexer is typically added to the system to control and access the plurality of video signals. In current systems, a multiplexer provides cost saving benefits by allow several cameras to share the same display and/or video recording device. However, the multiplexer does not reduce the number or cost of individual camera placements.
For example, U.S. Pat. No. 5,995,140 (the ""140 patent) discloses synchronization of a plurality of camera nodes from a single controller. The system disclosed in the ""140 patent uses a costly approach in which unique conductors are required for each video node requiring expensive wiring and a video switcher. The ""140 patent discloses the use of conventional CCD video cameras, such as the Sony model XE-75, which support external synchronization inputs and require expensive mounting hardware. Conventional external horizontal and vertical synchronization techniques are taught rather than the use of a single master frame synchronization signal driving low-cost camera chips which house digital synchronization circuitry as provided in the present invention as fully described hereinbelow.
A number of synchronized low-cost camera nodes sharing a single cable to reduce cost associated with wiring, installation, cameras, video multiplexer and mounting is provided.
In a first aspect of the present invention, a camera node for use in a multiple camera system with a common video conductor includes a sensor for converting light to an electrical video signal. A controllable driver for driving the electrical video signal onto a video conductor is enabled by an addressable output drive controller. A communication controller receives a unique address and sets the addressable output drive controller. A synchronization signal is received for enabling the controllable driver only at the start of a video frame and disabling the controllable driver only at the completion of a video frame.
The camera node synchronization can be provided externally from the camera node. The camera node synchronization enables the controllable driver only at the start of a video field and disables the controllable driver only at the completion of a video field.
In a second aspect of the present invention, a method for using a camera node in a multiple camera system having a common video conductor includes sensing and converting light to an electrical video signal; receiving the node""s unique address; synchronizing the driving only at the start of a video frame; driving the electrical video signal onto the video conductor only at the start of the next video frame; disabling the driving only at the completion of a video frame and only if a node address other than the node""s unique address is received.
The method can have the synchronizing provided externally from the camera node. The method can have the synchronizing enabling the driving only at the start of a video field and disabling the driving only at the completion of a video field.
In a third aspect of the present invention, a video surveillance system using a plurality of camera nodes includes an electrical cable connected to the camera nodes, the cable including conductors for conducting power, video, control, and synchronization signals to the camera node. The camera nodes each include a sensor for converting light to an electrical video signal, a controllable driver for driving the electrical video signal onto the video signal conductor, an addressable output drive controller for enabling the controllable driver, communication controller for receiving a unique address to set the addressable output drive controller, and synchronization for enabling the controllable driver only at the start of a video frame and disabling the controllable driver only at the completion of a video frame.
Objectives, advantages, and applications of the present invention will be made apparent by the following detailed description of embodiments of the invention.